1. Field of the Invention
The present invention relates to receivers which perform the dual functions of (a) determining their position by means of reception of transmission from global positioning satellite systems and (b) performing communications to and from other locations in order to receive position location commands and other information and transmit in return data representative of position information which was found through reception of transmissions from global positioning satellite systems.
2. Background Art
The combination of GPS systems and other communications systems is receiving considerable interest, especially in the areas of personal and property tracking. An example of such a combination is shown in U.S. Pat. No. 5,225,842. The communication link allows an inexpensive GPS (Global Positioning System) receiver located on a mobile person or object (for example, a vehicle or animal) to transmit its accurately determined position to remote locations which monitor this activity. Applications of this technology include security, truck fleet tracking, emergency response, inventory control, etc. The prior art has performed such combinations by mating separate GPS receivers and communication systems using suitable electronic interfaces between the two, for example, serial communication ports, etc. Common housings and a common power supply are often shared in order to reduce over all cost. Nevertheless, the prior art provides systems utilizing separate circuitry to perform the GPS and communication functions.
It has heretofore been impractical to combine much of the circuitry of the two different systems since all known GPS receivers utilize specialized hardware, called "correlators", to process the received signals from a multiplicity of satellites. This specialized hardware differs markedly from that used in communications receivers and transceivers such as cellular telephones and pagers. In many communication receivers, such as those found in cellular telephones and pagers, signal processing functions are performed using general purpose digital signal processing integrated circuits, such as the TMS 320 family from Texas Instruments. Accordingly, the signal processing hardware of the two different systems are incompatible in a combined GPS and communication system.